Uniplanar screw

ABSTRACT

A spinal screw assembly is provided. The assembly may be provided with a screw and a movable head in which angulation of the screw relative to the movable head is constrained so that angulation within limits is allowed in one plane but lesser or no angulation is allowed in another plane. Methods to assemble the disclosed apparatus are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit under 35 U.S.C. §119(e)to U.S. Provisional App. No. 61/362,993, filed on Jul. 9, 2010. Thisapplication is also related to U.S. patent application Ser. Nos.12/117,609; 12/117,615; and 12/117,613. The entire contents of theaforementioned applications are herein incorporated by reference intheir entirety.

TECHNICAL FIELD

Embodiments of the invention pertain to spinal surgery.

BACKGROUND

Spinal surgery frequently uses polyaxial pedicle screws that may allowangulation in various degrees of freedom between the movable screw headand the screw itself. Such screws may have a spherical screw headcaptured somewhere within the movable head. A uniplanar screw may beprovided that allows angulation in one plane but prevents or limitsangulation in another plane mutually perpendicular to the first plane.

SUMMARY

In an embodiment, there may be provided a spinal screw apparatus inwhich the movable head has a bottom opening shaped so as to allow moreangulation in a first angulation plane than in a second angulation planethat is perpendicular to the first angulation plane.

In another embodiment, there may be provided a spinal screw apparatus inwhich the movable head possesses a proximal portion and at least onedistal portion joined to the proximal portion, and the distal portionhas a mechanical interlock with the proximal portion.

In another embodiment, there may be provided a spinal screw apparatus inwhich the movable head possesses a proximal portion and two distalportions each joinable to the proximal portion.

Yet another embodiment may provide a spinal screw apparatus in which thescrew head and movable head each have at least one flat surface, and thecorresponding flat surfaces face directly toward each other.

In another embodiment, a spinal screw apparatus is provided with ascrew, a movable head, and a collet. The screw has a shaft or shank anda screw head. The screw head may be fixedly attached to the shaft orshank such that it is connected as a separate piece or may possibly beintegrated with the shaft or shank to be formed as a single piece. Themovable head may have a concave interior larger than the screw head. Thecollet may be interposed between the screw head and the concave interiorof the movable head. The movable head has a bottom opening shaped so asto allow more angulation around a first rotational direction than arounda second rotational direction that is perpendicular to the firstrotational direction.

Another embodiment provides a moveable head for a spinal screwapparatus. The movable head may be provided with a body having anopening therethrough. The opening may have an opening longitudinal axisand a proximal end and a distal end. The body may also have an internalsurface defining an internal cavity having a distal end openingperimeter. The body may also have a proximal component and at least onedistal component joined to the proximal component. The distal componentmay define at least a portion of the distal end opening perimeter. Thedistal component may have a mechanical interlock with the body.

Another embodiment provides a moveable head for a spinal screwapparatus. The movable head may be provided with a body having anopening therethrough. The opening may have an opening longitudinal axisand a proximal end and a distal end. The body may also have an internalsurface defining an internal cavity having a distal end openingperimeter. The body may also have a proximal component and at least onedistal component joined to the proximal component. The distal componentmay define at least a portion of the distal end opening perimeter. Thedistal component may have a first sub-motion-limiter that may bejoinable to the proximal component and a second sub-motion-limiter thatmay also be joinable to the proximal component.

Yet another embodiment provides a spinal screw apparatus that has ascrew and movable head. The screw may have a head and a shaft having ashaft axis. The screw head may be fixedly attached to the shaft suchthat it is connected as a separate piece or may possibly be integratedwith the shaft to be formed as a single piece. The screw head may beprovided with a portion of a sphere and may also have at least one flatexternal surface defining a plane substantially parallel to the shaftaxis. The movable head may capture the screw head. The movable head maybe configured to have a concave interior suitable to receive the screwhead with the interior having a flat interior surface. The flat interiorsurface may directly face the flat external surface.

In a disclosed embodiment, there may be provided a screw apparatushaving a movable head that has a groove or pair of grooves and receivesa motion limiter or a pair of motion limiters. One of the motionlimiters may be entirely to one side of the plane of a mid-plane of themovable head that contains an axis of a U-trough and a spinal rod, andthe other of the motion limiters may be entirely to the other side ofthe mid-plane.

In yet another embodiment, there may be provided a screw apparatus thatallows motion of the screw shaft relative to the movable head such thatthe motion is bounded by a shape that comprises a straight line segmentand a curved segment.

In yet another embodiment, there may be provided a collet that has slotson a rod-contacting surface thereof, such that the slots are oriented ina non-radial direction.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Embodiments are further described in the following illustrations.

FIG. 1 is a three-dimensional perspective view of a screw used in anembodiment.

FIG. 2 is a three-dimensional perspective view of a collet used in anembodiment.

FIGS. 3A, 3B and 3C are various three-dimensional perspective views of amovable head used in an embodiment.

FIG. 3D is a cross-sectional view of the embodiment shown in FIGS. 3A,3B, and 3C.

FIG. 4 is a three-dimensional perspective view of a set screw andsaddle, as used in an embodiment.

FIG. 5A is a three-dimensional perspective view of a screw assembly.

FIG. 5B is a cross-section of the embodiment shown in FIG. 5A.

FIG. 6A is a three-dimensional perspective view of a screw assemblyillustrating certain features regarding rotation and angulation of thescrew with respect to the movable head.

FIG. 6B is a side view of the embodiment shown in FIG. 6A.

FIG. 6C is a side view of the embodiment shown in FIG. 6A.

FIG. 7 is a perspective view of a movable head of a disclosedembodiment.

FIG. 8A is a perspective view of a cross-section of the movable head andthe screw and the collet, in the absence of the distal portion of themovable head.

FIG. 8B is a perspective view of a cross-section of the movable head andthe screw and the collet, in the presence of the distal portion of themovable head.

FIGS. 8C, 8D, 8E and 8F are various views, nearly along the axis, ofassemblies similar to those of FIGS. 8A and 8B.

FIG. 9A is a perspective view of only the distal portion of the movablehead, having two sub-motion-limiters.

FIG. 9B is a perspective view of only one sub-motion-limiter.

FIG. 10 is a perspective view of a sub-motion-limiter and a proximalportion of the polyaxial screw head, showing a sub-motion-limiter aboutto slide into place in the movable head.

FIG. 11 is a perspective view similar to FIG. 10, but from a differentviewing angle.

FIG. 12 is a perspective view similar to FIG. 11 but showing twosub-motion-limiters about to slide into place, from yet another viewingangle.

FIG. 13A is a perspective view of a sub-motion-limiter.

FIG. 13B is a perspective view of a sub-motion-limiter and also aproximal portion, illustrating respective taper angles.

FIG. 14A is a perspective view of a cross-section of a uniplanar screwassembly.

FIG. 14B is a close-up view of a portion of FIG. 14A.

FIG. 15 is a three-dimensional perspective view of a sub-motion-limiterand also a collet in a typical position relative to thesub-motion-limiter.

FIGS. 16A-16G are three-dimensional perspective cross-sectionalillustrations which show sequential steps in the assembly of a screw ofan embodiment.

FIG. 17A is a three-dimensional perspective view of a screw assembly ofan embodiment, together with a spinal rod.

FIG. 17B is a cross-section of FIG. 17A, along 17B-17B.

FIG. 18A is a three-dimensional perspective view of a screw of anotherdisclosed embodiment

FIGS. 18B and 18C are side views of the embodiment shown in FIG. 18A.

FIGS. 19A, 19B, and 19C are three-dimensional perspective views of theproximal portion of a movable head of an embodiment, each from adifferent vantage point.

FIG. 19D is a three-dimensional perspective view of the distal portionof the movable head, suitable to connect to the proximal portion of themovable head shown in FIG. 19C.

FIG. 20 is a three-dimensional perspective view showing the movable headshown in FIG. 19B and the bottom cap shown in FIG. 19C joined together.

FIGS. 21A and 21B are three-dimensional perspective views of a top-cappiece.

FIG. 22A is a three-dimensional cross-sectional view of an assembly of adisclosed embodiment.

FIG. 22B is a three-dimensional cross-sectional view of the assemblyshown in FIG. 22A from a different perspective.

FIG. 23 is a three-dimensional perspective view showing only the movablehead and the screw head.

FIG. 24 is a three-dimensional perspective view showing only the screwhead and the movable head distal portion.

FIGS. 25A-25D are three-dimensional perspective cross-sectional views ofthe apparatus in sequential stages of assembly.

FIG. 26 is a three-dimensional perspective view of an embodiment of ascrew.

FIG. 27A is a perspective view of the movable head of the embodimentshown in FIG. 26.

FIG. 27B shows the embodiment of FIG. 27A with the two motion limitersomitted for clarity.

FIG. 27C shows the embodiment of FIG. 27A with the movable head omittedfor clarity.

FIG. 27D is a perspective view of an embodiment of a motion limiter.

FIGS. 27E and 27F are perspective views of one embodiment of a motionlimiter being inserted into an embodiment of a movable head, while theother motion limiter is already in place in the movable head.

FIG. 28 is a composite view of the embodiment of a screw shown in FIG.26 showing multiple possible positions of the screw shaft relative tothe movable head.

FIG. 29A is a three-dimensional perspective view of a screw with a firstdesign of certain external features of the movable head.

FIG. 29B is a three-dimensional perspective view of a screw with asecond design of certain external features of the movable head.

FIG. 30A is a three-dimensional perspective view of an embodiment thatprovides D-planar motion.

FIG. 30B is a three-dimensional perspective view of the embodiment shownin FIG. 30A, with only the movable head shown for clarity.

FIG. 30C is a similar view to that of FIG. 30B.

FIG. 30D is a view similar to that of FIG. 30B.

FIG. 31A is a three-dimensional perspective view of the embodiment shownin FIG. 30A, but with the screw shaft shown in multiple positionssuperimposed on each other to illustrate a range of motion.

FIG. 31B is similar to FIG. 31A.

FIG. 32A is a three-dimensional perspective view of an embodiment of acollet.

FIG. 32B is a top view of the embodiment shown in FIG. 32A.

FIG. 32C is a perspective view of an embodiment of a screw apparatuswith the embodiment of the collet shown in FIGS. 32A and 32B.

DETAILED DESCRIPTION

Embodiments may further be understood with reference to the variousFigures. With reference to FIGS. 1, 2, and 3, an embodiment provides ascrew 100 that may possess a shaft 110, and a screw head 130 that may beintegral with or attached to the shaft 110. The screw head 130 may be aportion of a sphere or have a spheroidal shape. The apparatus mayfurther be provided with a collet 200 that may fit around all or aportion of the screw head 130. The apparatus may further have a movablehead 300, which may in turn fit around the collet 200.

Screw

Referring now to FIG. 1A and FIG. 1B in additional detail, screw 100 maypossess threads 120 around shaft 110. Screw head 130 may also have, atits end opposite shaft 110, a tool interface recess 136 (see, e.g.,FIGS. 16C-16F) that may be a hexalobe feature. Screw 100 may have alongitudinal axis 140. The longitudinal axis 140 generally extendsthrough the center of the screw 100 along its length. In the vicinity oflongitudinal axis 140, the screw shaft 110 may be either solid (asillustrated) or alternatively may be hollow, with the empty centralregion being available for other purposes as may be desired. Other thantool interface recess 136 and features related to threads 120, the screw100, including the screw head 130, may be axisymmetric aboutlongitudinal axis 140.

Collet

Referring now to FIGS. 2A and 2B, there may be provided with a collet200 having a generally ring shape defining a central opening 208 and alongitudinal axis 240. The collet 200 may have a first or top end at aproximal end 202 of the collet 200 and a second or bottom end at adistal end 204 of the collet 200. The collet longitudinal axis 240extends through the center of the collet 200 from a proximal end 202 toa distal end 204 of the collet 200. The collet 200 may have slots 210that may be provided in an alternating pattern around the circumference.Such a slot pattern may provide the collet 200 with the ability toelastically deflect in any of various directions. For example, thecollet 200 may, within certain limits, be deformable radially inwardlyand may be deformable radially outwardly. Bending or twisting of thecollet 200 in various directions may also be permitted.

It is further possible that the collet 200 may, when in an undeformedstate, have a collet inner surface 220 that may be partially sphericaland may resemble a portion of the external surface of the screw head130. However, the collet inner surface 220 does not need to exactlymatch the external surface of the screw head 130. More generally, thecollet inner surface 220 may be concave with a less tight curvature(that is, a larger radius of curvature) than the spherical portion ofthe screw head 130. The collet inner surface 220 and the screw head 130may be related to each other such that when the collet 200 isconstrained against outward radial deformation, the screw head 130 isprevented from sliding distally with respect to the collet 200, such asby a wedging action. For example, as illustrated in FIG. 2B, the insidesurface of the collet 200 may have an inside radius (measured fromcenterline axis 240) of R1 near the proximal end 202, and may haveanother inside radius R2, and may have a third inside radius R3 near thedistal end 204. R2 may be measured somewhere between the measurementlocations of R1 and R3. R2 may be the largest radius of the three radii.Also, the exterior of the collet 200 may have an external taper 201 orcurvature such that the collet exterior is narrower toward the distalend 204 of the collet 200 as compared to the proximal end 202 of thecollet 200.

It is further possible that the collet 200 may have a collet externalsurface 230, which may resemble an internal surface 325 of the movablehead 300. At least a portion of the collet external surface 230 may befrustoconical. In FIG. 2B, the overall included angle of the externaltaper of collet 200 is labeled using the designation a (alpha). However,the collet external surface 230 need not exactly match internal surface325 of movable head 300 or any other internal surface of the movablehead 300.

The collet 200 may be capable of deforming radially outwardly so as toreceive the screw head 130, and may be capable of springing radiallyinwardly after the screw head 130 is in an appropriate place inside thecollet 200.

The collet 200 and screw head 130 may be related such that when thecollet 200 fits around the screw head 130 in the absence of movable head300, with no external forces being applied, the collet 200 is snugagainst the screw head 130 resulting in friction between the collet 200and screw head 130. The collet 200 and screw head 130 may be relatedsuch that when the collet 200 fits around the screw head 130 in thepresence of movable head 300 in the fully-assembled configuration butwithout a spinal rod tightened into place, the collet 200 is snugagainst the screw head 130 resulting in friction between the collet 200and the screw head 130. This friction may be such that the movable head300 can be placed in any desired position relative to the screw 100within the range of permitted motion and will remain in that position atleast against gravitational forces acting on the various parts of thescrew assembly (i.e., the individual weight of the various parts) in anyorientation. The friction may be greater than what is needed simply tomaintain a position of the screw 100, relative to the movable head 300,against gravitational forces.

The collet 200 may further have an external lip 250 at or near itsproximal end. Such an external lip 250 may extend farther outwardly in aradial direction than the rest of the collet 200. The external lip 250may be interrupted by the slots 210 just as nearby parts of the collet200, other than the external lip 250, are interrupted by the slots 210.

Movable Head

Referring now to FIGS. 3A-3D, movable head 300 may have a proximal end302 and a distal end 304 and a generally longitudinal axis 340 from theproximal end 302 to the distal end 304 through the center of the movablehead 300. The movable head 300 may also have a first or top portion orend and a second or bottom portion or end, whereby the top portion islocated at a proximal end 302 of the movable head 300 and the bottomportion is located at a distal end 304 of the movable head 300. Themovable head 300 may have an internal thread 310 at its proximal end302. The movable head 300 may also have, at its proximal end 302, aU-shaped passageway or U-trough 360 through the movable head 300. TheU-trough 360 may have an axis generally perpendicular to thelongitudinal axis 340 of the movable head. The U-trough 360 axis mayalso be generally transverse through the movable head 300. The movablehead 300 may have a hole 365 therethrough at its distal end or bottomportion.

The movable head 300 distal end 304 may have an internal surface 320located between the internal thread 310 and the hole 365 at the distalend 304. The internal surface 320 may be generally concave and may be atleast partially spherical or generally spheroidal in shape. Asillustrated in FIG. 3D, the movable head 300 may have an internal lip350 between the internal surface 320 and the internal thread 340. Themovable head 300 may also have an internal tapered region 325, which maybe frusto-conical and may be at least somewhat complementary to theexternal surface 230 of the collet 200.

There may be provided, on an external surface of the movable head 300,any of a variety of interface features 390 a, 390 b for interfacing witha tool or instrument. Such interface features 390 a, 390 b may beprovided on each of two opposed sides of the movable head 300. Theinterface features 390 a, 390 b may be identical to each other orsymmetrical to each other about a common plane or axis, or,alternatively, there may be design differences between the interfacefeatures 390 a and 390 b. It is possible that either or both of theinterface features 390 a, 390 b may have an undercut so as to provide aslip-resistant interface with the instrument or tool. As is illustratedmost particularly in FIG. 3B, such an undercut may have across-sectional shape that is trapezoidal, with base 391 a, the longerof the two parallel sides of the trapezoid and being closer to thelongitudinal axis 340 of the movable head 300 than is opening 391 b, theshorter of the two parallel sides. As illustrated most particularly inFIG. 3C, it is possible that either or both of the interface features390 a, 390 b may have an external interface centering feature 392 thatis located at a plane of symmetry of the movable head 300. The externalinterface centering feature may be a depression or may be a recess in adirection different from other portions of the interface features 390 a,390 b.

Movable head 300 may also possess a proximal portion or component 370and a distal portion or component 380, as described in more detailelsewhere herein.

Set Screw and Saddle

Referring now to FIG. 4, the apparatus may further be provided with aset screw 500 that may have an external thread 540 that engages with theinternal thread 310 of the movable head 300. The apparatus may furtherbe provided with a saddle 580 to form an interface between the set screw500 and a rod 400 (described elsewhere herein). The saddle 580 may becaptured by or attached to set screw 500 in such a way as to form asingle assembly together with the set screw 500. However, even whencaptured or assembled, the saddle 580 may be able to rotate with respectto the set screw 500. Such capturing or assembly connection may beeither loose or frictional as desired. Furthermore, it is possible thatwhen the assembly of the saddle 580 and set screw 500 is provided to theuser, the relative rotational position of the saddle 580 and set screw500 may be pre-set so as to be appropriate for starting engagement ofthe thread of the set screw 500 with the thread 310 of the movable head300. This thread-starting relationship is especially achievable if thereis a frictional relationship between the saddle 580 and set screw 500.Thus, sliding the saddle 580 into the U-trough 360 may then serve toalign the threads to their proper starting position. The rod-facingsurface 590 of the saddle 580 may be at least approximately contoured tocomplement the corresponding surface of the rod 400 so as to provideappropriate transfer of clamping load and other loads to or from the rod400. The rod-facing surface 590 of the saddle 580 may be either smoothor textured as desired. The external shape of the saddle 580 may be suchthat the saddle 580 can only be slid into the movable head 300 atcertain angular positions, which may correspond to desiredthread-starting positions.

It is further possible that there could be provided timing featuresmarked on any of the nearby parts for indicating the optimal place tobegin engagement of the set screw thread 540 and the internal thread 340in the movable head 300.

Assembled (but Un-Tightened) Apparatus

These various components are shown in FIGS. 5A and 5B in a configurationin which the components have been assembled, but the apparatus is notyet tightened so as to hold a spinal rod. This may be referred to as anominal assembled configuration. It is noted that, as illustrated inFIGS. 5A and 5B, the collet 200 is not as far advanced toward the distalend of the apparatus as it would eventually be when a rod 400 is inplace and tightened. Also as illustrated in FIGS. 5A and 5B, the collet200 is positioned such that the external lip 250 of the collet 200 isjust slightly distal of the internal lip 350 of the movable head 300(also shown in FIG. 16D-16F).

Rotation and Angulation

Referring now to FIGS. 6A-6C, a configuration of the apparatus isprovided showing the position of the screw with respect to the movablehead 300, with a screw assembly of an embodiment tightened to grasp aspinal rod 400.

Referring now to FIG. 6A, the illustrated apparatus shows the screw 100is able to rotate with respect to the movable head 300 around thelongitudinal axis 140 of the screw 100. The apparatus may be such thatthe screw 100 is able to rotate about the longitudinal axis 140 withoutconstraint, i.e., even more than one full rotation if desired. It ispossible, although it is not wished to be limited to this example, thatwhen such motion occurs, the screw head 130 rotates with respect to thecollet 200 while the collet 200 remains stationary with respect to themovable head 300. However, it is also possible that the opposite mayhappen, i.e., the screw head 130 and the collet 200 could rotate as aunit with respect to the movable head 300. Furthermore, it is evenpossible that some rotation at each interface could occur.

It can further be observed that for the apparatus as illustrated, thescrew head 130 is able to angulate with respect to the movable head 300around at least one additional axis that is not coincident with thescrew longitudinal axis 140. However, there may be constraints againstsuch angulation in certain directions, as described below.

Limits on Angulation

With continuing reference to FIGS. 6A-6C, the apparatus may beconfigured such that it permits, within certain limits, angulation ofthe screw 100 with respect to movable head 300. The limits of angulationmay be such as to define a space of permitted angles that make up ashape which is not a cone. The limits of angulation may be defined quitespecifically by the shape of the edges of the distal portion 380 of themovable head 300 (such as sub-motion-limiters 382, 384). Angulationlimits may be defined with respect to each of two different planes orrotational axes, which may be mutually perpendicular to each other.These amounts of angulation may be, and preferably are, different fromeach other. As illustrated in FIG. 6B and FIG. 6C, a substantial amountof angulation of the screw 100 relative to the movable head 300 ispermitted in the degree of freedom illustrated in FIG. 6B, while littleor no angulation of the screw 100 relative to the movable head 300 ispermitted in the degree of freedom illustrated in FIG. 6C.

Referring now to FIG. 6B, it is further possible that the axis of therod 400 may lie in or may be parallel to the defined plane of angulationin which substantial angulation is permitted. However, it is alsopossible that there could be other relations between the plane ofsubstantial permitted angulation and the axis of the spinal rod 400.

It is further possible that there may be defined a baseline position ofthe movable head 300 relative to the screw longitudinal axis 140 suchthat the longitudinal axis 340 of the movable head 300 might, when inthis baseline position, coincide with the screw longitudinal axis 140,as is illustrated in FIGS. 8A, 8B and 12. This baseline position mayalso be such that the screw is in all respects in the middle of therange of permitted angulation positions. However, it is not essentialthat the longitudinal axis of the movable head 300 coincide with themiddle of the range of angulation. If desired, it may also be possibleto design the screw assemblies such that the baseline position of themovable head axis 340 is biased. In other words, the baseline positiondoes not have to be coincident with the screw longitudinal axis 140 atthe middle of the range of angulation.

Details about Angulation-Limiting Components

Referring now to FIG. 7, the movable head 300 may be provided with aproximal portion or component 370 and a distal portion or component 380that may be assembled to each other for purposes of achieving limits ofangulation of the screw shaft 130. It is possible that distal portion380 could be made as a single component if appropriate provision is madefor joining the distal portion 380 to the proximal portion 370. Forexample, the distal portion 380, if made as a single component, might bewelded to the proximal portion 370 but without the benefit of amechanical interlock, i.e., with the weld being the major path fortransferring mechanical load from distal portion 380 to proximal portion370.

The distal portion 380 will be first discussed as a single component.The opening through the distal portion 380 may help to determine thepermitted angulation of the screw shaft 130 with respect to polyaxialthe screw head 300. The distal portion 380 may define a distal opening365 through the movable head 300. The distal opening 365 may have anon-round shape. For example, the distal opening may have an elongatecircular or racetrack shape. The distal opening 365 may be such thatwhen the various components are assembled, the distal opening 365 limitsangulation of the screw 100 relative to movable head 300. The distalopening may be such as to permit angulation within defined limits withina first plane and essentially forbid angulation in a second plane thatis perpendicular to the first plane. Alternatively, the distal openingmay be such as to permit a defined amount angulation in a first planeand permit only a relatively smaller defined amount of angulation in asecond plane that is perpendicular to the first plane.

FIG. 8A shows proximal portion 370 and the screw head 130, but distalportion 380 is not shown. FIG. 8B shows proximal portion 370, distalportion 380 and the screw head 130.

FIGS. 8C-8F, show, for purposes of illustration, the arrangement ofmovable head 300 and the screw 100, with the collet 200 omitted forclarity of illustration. These illustrations are views approximatelyalong the axis 140 of the screw 100. FIGS. 8C and 8D are views lookingfrom the proximal end to the distal end, and FIGS. 8E and 8F are viewsfrom the distal end to the proximal end. In FIG. 8C, thesub-motion-limiters 382, 384 are omitted and it can be observed thatthere is empty space completely around the screw head 130 between themovable head 300 and the screw head 130, which illustrates that thescrew head 130 has an unrestricted path to come up into the movable head300 for assembly purposes. The same situation is visible in FIG. 8E froma different vantage point. In FIG. 8D, the two sub-motion-limiters 382,384 are present, and a small visible portion of sub-motion-limiters 382,384 is highlighted. In FIG. 8F, from a different vantage point,sub-motion-limiters 382, 384 are visible in their entirety, andtherefore empty space is visible at only some places around thecircumference of the screw head 130, but is not visible around theentire circumference of the screw head 130. In FIGS. 8D and 8F, emptyspace is visible between the movable head 300 and the screw head 130 intwo places but not all the way around the circumference. The empty spacewhich is visible is related to the range of permitted motion. The placeswhere empty space is not visible are related to the trapping of thescrew head 130 within movable head 300. In this situation, thesub-motion-limiters 382, 384 may contribute to trapping the screw head130 within the movable head 300, although the collet 200 (not present inFIG. 8C-8F) may also be involved in direct contact with the screw head130.

Referring now to FIGS. 9A and 9B, it is possible that the distal portion380 may be provided with two sub-motion-limiters 382, 384 which togethermake up distal portion 380. The sub-motion-limiters 382, 384 may beidentical to each other, or symmetric to each other about a common planethat generally lies between the sub-motion-limiters 382, 384 so thateach one makes one-half of distal portion 380. Such subdividing ofdistal portion 380 into sub-motion-limiters 382, 384 may be done such asto facilitate assembly as discussed elsewhere herein.

Referring now to FIG. 10, the interaction between the sub-motion-limiter382 and the polyaxial the screw head proximal portion 370 is shown. Thesub-motion-limiter 382 is adapted to slide, along a direction of slidinginsertion, into a receiving feature in the proximal portion 370 of themovable head 300. The direction of sliding insertion is generallyparallel to an axis through the U-trough 360 (an axis generallyfollowing a longitudinal axis of rod 400 as shown at least in FIG. 6A),and also generally perpendicular to the longitudinal axis 340 of themovable head 300. Though, this example is not intended to be limiting,for instance, the direction of sliding insertion may be skew to an axisof the U-trough, or at an angle to the longitudinal axis 340 of themovable head that is less than perpendicular. FIG. 10 is a perspectiveview, in which sub-motion-limiter 382 is positioned some distance behindthe movable head 300. As a result, the sub-motion-limiter 382 appearsnarrower in width than a corresponding dovetail feature in the movablehead 300. However, this only appears as such because of the perspectivenature of the illustration, and the orientation of the view. The designof the sub-motion-limiter 382 and the design of the proximal portion 370may be such that the sub-motion-limiter 382 is mechanically capturedwithin the proximal portion 370. Such geometry could thereby restrainthe sub-motion-limiter 382 against possible motion or forces along thelongitudinal axis 340 of the movable head 300, such as forces that wouldact to separate the sub-motion-limiter 382 from the proximal portion370. In some embodiments, the interaction between sub-motion-limiter 382and proximal portion 370 may have a dovetail joint. For example, thesub-motion-limiter 382 (or 384) may have a taper such that thesub-motion-limiter 382 is wider at its proximal end and narrower at itsdistal end, and the proximal portion 370 of the movable head 300 mayhave a complementary taper, such as, for example, a dovetail feature372. As a result of these tapers, the sub-motion-limiter 382 (or 384)and the proximal portion 370 may form a dovetail joint connectioncapable of resisting separation that could be caused by forces appliedto the distal portion 380 along the longitudinal axis 340 of the movablehead 300. Of course, as an alternative to the dovetail joint 372, ashelf relationship, such as a shelf or step joint, could also be usedfor the same purpose. Clips or other retention features could beprovided so that when the sub-motion-limiter 382 (or 384) is in place inthe proximal portion 370 it is discouraged from coming out of place. Itwould also be possible that there be a press fit between any of therelevant components to retain the components in place. Similarly, itwould be possible that some deformation is required to occur in orderfor the components to be assembled. Welding, such as laser-welding,could also be used in attachment of sub-motion-limiter 382 (or 384) tothe proximal portion 370 either in addition to the described mechanicalinterlock, or in place thereof.

FIG. 11 also illustrates the ability of the sub-motion-limiter 382 toslide into the proximal portion 370, but viewed from a differentperspective. FIG. 12 also illustrates this, but shows bothsub-motion-limiters 382 and 384 as if they were about to slide intoplace (also showing the screw 100 already in position).

Referring now to FIGS. 13A and 13B, there is further illustrated thepossible taper or dovetail relationship between sub-motion-limiter 382or 384, and proximal portion 370, particularly dovetail 372. FIG. 13A isa view of sub-motion-limiter 382, showing the taper angle. FIG. 13B is aview of sub-motion-limiter 382 and also proximal portion 370 with taperangles identified on both pieces. It can be seen that the taper angleson the respective pieces 382 and 370 are equal to each other or, moregenerally, are almost equal to each other.

Referring now to FIGS. 14A, 14B and 15, the distal portion 380 orsub-motion-limiters 382, 384 may have a recess 394 suitable to providespace for a portion of the collet 200. If there are sub-motion-limiters382, 384, each of the sub-motion-limiters may have such a recess. Therecess 394 may be such that when all the components are assembled, thereis a gap between the most-distal end surface of the collet 200 and thefacing surface of the recess 394 in the sub-motion-limiter. Thus, theremay be provided room for the collet 200 to find its tightened positionas determined by the wedging of the collet 200 external surface againstthe internal surface of distal portion 380 (sub-motion-limiters 382,384) of movable head 300. It is also illustrated in FIG. 15 that thesub-motion-limiters 382, 384 may have a stop feature 388 that cooperateswith the proximal portion 370 to determine how far towards thecenterline 340 the sub-motion-limiters 382, 384 are allowed to slide.Thus, the stop feature 388 may determine the final position ofsub-motion-limiters 382, 384 relative to proximal portion 370,especially in a direction along the direction of motion by whichsub-motion-limiters slide into their final position in proximal portion370.

The various parts may fit together such that in a fully assembled andtightened condition, a force from the set screw 500 is exerted (possiblythrough the saddle 580) onto a spinal rod 400, which in turn exertsforce onto the proximal end surface 250 of the collet 200 which urgesthe collet 200 farther into the tapering interior of proximal portion370. This may create a wedging action involving the interior of theproximal portion 370, the collet 200, and the screw head 130. Such awedging action may lock all of the relevant components into a fixedposition.

The apparatus may further have a joint, such as, for example, a weld forjoining the sub-motion-limiter 382, 384 and the proximal portion 370,but such joint need not carry all of the force transmitted through thejoint because of the presence of a dovetail relationship or similarsupporting relationship between the sub-motion-limiter 382, 384 andproximal portion 370.

Dimensional Interrelationships and Sequence of Assembly

The apparatus may have features that provide for mechanically trappingthe collet 200 within the movable head 300 when the collet 200 is deeperthan a certain point within the movable head 300. For example, theinternal lip 350 may be such as to interact with the external lip 250 ofthe collet 200 so as to trap the collet 200 inside the movable head 300.In order for the external lip 250 of the collet 200 to pass by theinternal lip 350, as the collet 200 moves toward the distal end of themovable head 300, it may be possible for the external lip 250 and thecollet 200, in general, to deform radially inwardly towards thelongitudinal axis 240 of the collet 200. It is also possible that afterthe external lip 250 passes the internal lip 350, moving in a directiontoward the distal end of movable head 300, the external lip 250 mayspring radially outwardly. This outwardly springing action may trap thecollet 200 inside the movable head 300, or at least may help to define apreferred or maintained position of the collet 200 relative to themovable head 300 when the collet 200 is in that region of the movablehead 300.

The apparatus may be such that the screw (particularly the screw head130) may be loaded into the movable head proximal portion 370 from thedistal end when the distal portion 380 or the sub-motion-limiters 382,384 are absent from the apparatus. More specifically, the diameter ofthe sphere of the screw head 130 may be smaller than an opening in thedistal end of the movable head 300, when the distal portion 380 or thesub-motion-limiters 382, 384 are absent from the apparatus. Thedimensions of the various components may further be such that when thedistal portion 380 or the sub-motion-limiters 382, 384 are together withthe rest of polyaxial the screw head 300, the sphere of the screw head130 cannot fit through the distal end opening of the apparatus. It isfurther possible that the sphere of the screw head 130 may be too largeto fit through the opening in the proximal end of the proximal portion370.

Dimensional interrelationships among the various components may be suchthat, when the distal portion 380 is absent, the screw head 130 may beable to pass upwardly through the opening 365 in the distal end of theproximal portion 370 of the movable head 300. Furthermore, when thedistal portion 380 is in place connected to the proximal portion 370 ofthe movable head 300, the screw head 130 may be unable to pass throughthe opening in the distal portion 380; but the screw shaft 110 is ableto pass through the hole in the distal portion 380. It is possible thatthe screw head 130 is unable to pass through the most proximal end ofthe collet 200 (the end having lip 250) when the collet 200 is in placeinside the movable head 300.

The collet 200 may be able to enter the movable head 300 through theopen proximal end of the movable head 300.

Referring now to FIG. 16A through FIG. 16G, it is possible that thefollowing assembly sequence may be used to assemble the describedcomponents:

1. As is shown in FIG. 16A, the proximal portion 370 of the movable head300 is provided without its distal portion 380.

2. Referring now to FIG. 16B, the collet 200 is introduced through theproximal end 302 of the proximal portion 370 of the movable head 300.The collet 200 is brought partially into the movable head 300 but isstopped before external lip 250 of the collet 200 passes the internallip 350 of the movable head 300. This may be termed a screw-receivingposition of the collet 200.

3. With reference to FIG. 16C, with the collet 200 in thescrew-receiving position, the screw head 130 is brought up through thedistal end 304 opening of the movable head 300. The screw head 130 isbrought into the collet internal space where it is received, whichrequires some elastic deformation of the collet 200.

4. Referring now to FIG. 16D, the collet 200, with the screw head 130already received inside it, is then advanced farther distally into themovable head 300 so that the external lip 250 of the collet 200 passesthe internal lip 350 of the movable head 300, and the collet 200 reachesits assembled position, in which the collet external lip 250 is moredistal than the internal lip 350.

5. Referring to FIG. 16E, sub-motion-limiters 382, 384 are brought intoposition at the distal end of the movable head 300. Because the bottomshoulder has sub-motion-limiters 382, 384, one sub-motion-limiter can bebrought in from each of two opposed directions. If thesub-motion-limiters and the main body of the movable head 300 arerelated by means of a dovetail or mechanical interlocking relationship,this feature may provide mechanical support. For clarity ofillustration, the proximal portion 370 and the screw 100 are shownsectioned, but the sub-motion-limiters 382, 384 are shown in theirentirety. It is also illustrated in FIG. 16E that thesub-motion-limiters 382, 384 may have a stop feature 388 that cooperateswith the screw shaft 110 to limit the motion of the screw shaft 110relative to the movable head 300.

6. In FIG. 16F, the sub-motion-limiters 382, 384 are joined to the mainbody of the movable head 300, such as by welding. At this stage ofassembly, as described elsewhere herein, there may be friction such thatthe movable head 300 may be placed in any desired position relative tothe screw 100, within the range of permitted motion, and will remain inthat position at least against gravitational forces acting on thevarious parts of the screw assembly (i.e., the individual weight of thevarious parts), in any orientation. The friction may be greater thanwhat is needed simply to maintain a position against gravitationalforces.

7. Next, referring now to FIG. 16G and also to FIGS. 17A and 17B, whenthe assembly is being implanted into a patient and a spinal rod 400 isbeing clamped by tightening of set screw 500 pressing against spinalrod, the spinal rod may press against the top of the collet 200, whichmay further urge the collet 200 or the screw head 130 or both into afinal-tightened position, which may be advanced farther distally withinthe movable head 300 as compared to the assembled position. In FIG. 16G,for clarity of illustration, the spinal rod 400 is not shown. Theposition of the collet 200 along the proximal-distal direction can bejudged, for example, by the position of the collet lip 250 relative tothe bottom of the U-trough 360 or relative to the internal lip 350.These positions differ from FIG. 16F to FIG. 16G. The final clampedposition is also illustrated in FIGS. 17A and 17B. A detail concerningthe final-tightened position relates to the collet 200 having an angularposition around its own longitudinal axis 240, which may be arbitrary,with respect to the movable head 300. More specifically, it is possibleeither that the spinal rod 400 presses against the external lip 250 ofthe collet 200, or that the spinal rod presses against the gap 210 inthe external lip 250 of the collet 200. The choice of lip contact or gapcontact can make a slight difference in the actual axial position of thecollet 200, along its own axis 240, when the whole assembly istightened. However, the difference will not be very large. In thetightened position as illustrated, the spinal rod 400 may bear againstthe lip 250 of the collet 200 and may be out of contact with the screwhead 130. Clamping of the screw head 130 may be achieved by frictionalgripping of the collet 200 against the screw head 130. However,depending on design details, other options may also be possible. Otherassembly sequences are also possible. For example, there is some freedomas to when one performs the step of advancing the collet 200, with thescrew head 130 already received inside it, farther distally into themovable head 300 so that external lip of the collet 200 passes internallip 350. Such step could be performed either before or after assembly ofthe sub-motion-limiters 382, 384 onto proximal portion 370.

As illustrated in FIGS. 14A, 14B and 15, the sub-motion-limiters 382,384 (or distal portion 380) may have a recess therein for receiving aportion of the collet 200. The collet 200 need not bear against therecess in distal portion 380 or sub-motion-limiters 382, 384, but therecess 394 may nevertheless be provided to allow space that can beoccupied by a portion of the collet 200.

Apparatus in Tightened Configuration

Referring now to FIGS. 17A and 17B, there is further shown the assemblyof the components of all previous Figures. Referring to FIG. 17A, thereis shown the previous assembly having the screw 100, the collet 200 andthe movable head 300, together with a segment of a rod 400, such as aspinal rod, seated in the movable head 300. As illustrated, a set screw500, and possibly saddle 580, is tightened against rod 400, rod 400bears against the proximal surface of the collet 200. It is possiblethat there may be differences in position of the collet 200 between anominal assembled configuration and a final tightened configuration. Itis possible that in the final tightened configuration, the collet 200may be more deeply (more distally) located within the movable head 300than is the case for the nominal assembled configuration. For example,between the nominal assembled configuration and the final tightenedconfiguration, the collet 200 may undergo some elastic deformation.However, this is dependent on design details and is optional.

As the rod 400 approaches or touches the bottom of the U-trough 360, itis possible that the rod 400 may also touch the bottom of the U-trough360, but that is optional and depends on design details.

As illustrated in FIG. 17B, the rod 400 does not touch the upper surfaceof the screw head 130. However, these are merely one of severalavailable design options. In general it is possible that, in a tightenedcondition, the rod 400 might touch any or all of: the bottom of theU-trough 360; the proximal surface of the collet 200; and the uppersurface of the screw head 130; or more than one of these in anycombination thereof.

Referring now to FIGS. 18A-18C, yet another embodiment may achieveuniplanar motion using a different embodiment than as previouslydisclosed in which the screw head possesses a pair of flat surfacesrather than being generally axisymmetric about its own centroidal axisas in the embodiment previously described. This alternate embodiment maybe provided with a screw 1100. The screw 1100 may have a shaft 1110 anda screw head 1130 integral with or joined to the shaft 1110. The screw1100 may have a longitudinal axis 1140.

In this embodiment, the screw head 1130 may have a portion of a spherebut furthermore may have two planar surfaces 1188 that may be opposed toeach other. The planar surfaces 1188 may be parallel to each other andmay be equally spaced on opposite sides of the longitudinal axis ofshaft of the screw 1100.

Referring now to FIGS. 19A-19D and 20, the embodiment may furtherprovide a movable head 1300. The movable head 1300 may have a proximalportion 1700 and a distal portion 1800 that may be connected to orjoined to each other or may be suitable to attach to each other.

The proximal portion 1700 of the movable head 1300 may have a U-trough1360 therethrough suitable to receive a spinal rod. The proximal portion1700 of the movable head 1300 may also have an axial opening 1365extending from its proximal end to its distal end. The axial opening1365 may merge with the open space of the U-trough 1360. The axialopening 1365 may be large enough for the screw head 1130 to pass throughthe distal end of proximal portion 1700. The axial opening 1365 may benon-circular. Portions of the axial opening 1365 may be suitable tointeract with the planar surfaces 1188 of the screw head 1130.

The distal portion 1800 of the movable head 1300 may have an internalsurface that is dimensioned suitably to bear against and retain thedistal-facing surface of the screw head 1130. The distal portion 1800 ofthe movable head 1300 may have an opening 1865 therethrough, throughwhich the screw head 1130 is unable to pass. This opening 1865 may becircular as illustrated, although it could be non-circular if desired.The opening 1865 facing distally may have a chamfer or othertransitional feature. The distal portion 1800 of the movable head 1300may be such as to limit angulation of the screw 1100 with respect to themovable head 1300. The distal portion 1800 of the movable head 1300 maybe axisymmetric about its own centroidal axis.

Referring now to FIGS. 21A and 21B, the apparatus may further have aforce-transmitting cap 1900. The force-transmitting cap 1900 may have adistal surface 1920 that is at least partially spherical and compatiblewith the spherical external surface of the screw head 1130. Theforce-transmitting cap 1900 may have a proximal surface 1930 that is atleast partially cylindrically compatible with a cylindrical spinal rod.The force-transmitting cap 1900 may possess a hole 1965 therethroughthat generally connects the distal surface 1920 and the proximal surface1910. The hole 1965 may be of larger diameter or cross-sectionaldimension than an instrument-receiving interface 1136 in the screw 1100.The force-transmitting cap 1900 may have side surfaces 1950 a, 1950 bthat may be substantially flat and parallel and suitable to fit betweencorresponding surfaces of the proximal portion of the movable head 1300.The force-transmitting cap 1900 may further be provided with a shoulder1642, and the proximal portion of the movable head 1300 may possess arecess suitable to receive the shoulder 1642 of force-transmitting cap1900. The force-transmitting cap 1900 may in some dimension be largerthan axial opening through the distal portion 1800 of the movable head1300. As a result, when the apparatus is fully assembled, theforce-transmitting cap 1900 may be trapped and unable to exit proximallybecause of the shoulder causing it to be trapped within the proximalportion 1400 of the movable head 1300, and unable to exit distallybecause of being trapped by the distal portion 1800 of the movable head1300.

When the apparatus is assembled and implanted in a patient, the variouscomponents may be such that a set screw engages threads in the proximalportion 1700 of the movable head 1300 and presses on the spinal rod,which in turn presses on the force-transmitting cap 1900, which in turnpresses on the screw head 1130. Forces from the screw head 1130 are inturn reacted by the distal portion 1800 of the movable head 1300, whichis in turn connected to the proximal portion 1700 of the movable head1300.

Referring now to FIG. 22A and FIG. 22B, there are shown cross-sectionsof the assembled apparatus. FIG. 22A is a cross-section taken in a planethat includes the spinal rod 1400, and FIG. 22B is a cross-section in aplane perpendicular to the spinal rod 1400. In FIG. 22A and in FIG. 22B,it can be seen that force-transmitting cap 1900 presses on the screwhead 1130. It can be noted that some of the force-transmitting cap 1900may protrude slightly into the space within the U-trough 1360, beyondthe interior surface itself of the U-trough 1360 itself. This enablesthe spinal rod to exert force directly on the force-transmitting cap1900, which in turn exerts force on the screw head 1300, to lock theposition of the screw 1100 with respect to the movable head 1300. InFIG. 22B, the flat sides 1188 of the screw head 1130 are also visible.Flat sides 1188 interact with corresponding flat surfaces in proximalportion 1700 to limit angulation of the screw head 1130 in a certaindegree of freedom of motion.

Referring now to FIG. 23, there is illustrated an assembly omitting theforce-transmitting cap 1900. This illustrates the shape into which theforce-transmitting cap 1900 fits. Referring now to FIG. 24, there isillustrated distal portion 1800 and the screw 1100. This illustratesthat the distal portion 1800 traps the screw head 1130.

FIG. 25A-25D show steps of assembly of the apparatus of this embodiment.FIG. 25A shows only the proximal portion 1700 of the movable head 1300as a first step of assembly. As a second step of assembly, FIG. 25Bshows the proximal portion 1700 of the movable head 1300, together withthe force-transmitting cap 1900. It can be noted that theforce-transmitting cap 1900 is introduced into proximal portion 1700through the distal end of proximal portion 1700, and is not able totravel all the way through the proximal portion 1700, so that it laterbecomes trapped within the assembly. As a third step of assembly, FIG.25C shows the proximal portion 1700 of the movable head 1300 togetherwith the force-transmitting cap 1900 and the screw 1100. As a final stepof assembly, FIG. 25D shows the components already illustrated in FIG.25C, together with the distal portion 1800 joined to proximal portion1700. The joining of the distal portion 1800 to proximal portion 1700traps the screw head 1130 and also traps the force-transmitting cap1900.

Alternate Design of Motion Limiters

Referring now to FIGS. 26-27D, there is illustrated another embodimentof the invention. FIG. 26 shows an assembly comprising a screw 2100including a screw shaft 2110, a collet 2200, and movable head 2300. Themovable head 2300, shown in more detail in FIGS. 27A-27D, may containwithin itself two motion limiters 2382, 2384. The first motion limiter2382 and the second motion limiter 2384 may occupy respective grooves2372, 2374 in the movable head 2300. The grooves 2372, 2374 may have alongitudinal axis that may be generally parallel to a longitudinal axisof the U-trough 2360 that extends through the movable head 2300, and mayalso be generally parallel to the longitudinal axis of the spinal rod400 that would be received within the U-trough 360 of the movable head300. As illustrated, there is one groove 2372, 2374 on each side of themid-plane of the movable head 2300, and the two grooves 2372, 2374 aresubstantially parallel to each other. Groove 2372 and groove 2374 may besymmetric about a common plane to each other.

A first motion limiter 2382 may be generally long and located withingroove 2372 and located entirely on one side of the plane that is amid-plane of the movable head 2300, corresponding to the spinal rod 400.A second motion limiter 2384 may be generally long and located entirelyon the other side of the plane in groove 2374. The first motion limiter2382 and the second motion limiter 2384 may be symmetric about a commonplane to each other.

The respective grooves 2372, 2374 in the movable head 2300 may comprisedovetail features, and the motion limiters 2382, 2384 may have externaltaper features corresponding to a dovetail joint. In particular, thegrooves 2372, 2374 may be wider at the top than at the bottom (in theorientation shown), and the motion limiters 2382, 2384 may be wider atthe top than at the bottom (in the orientation shown). The taper angleof the dovetail feature of the groove 2372, 2374 is illustrated in FIG.27B, and a taper angle of the motion limiter 2382, 2384 is illustratedin FIG. 27C. These two taper angles may be equal to each other, althoughit is not necessary that they be exactly equal to each other. As aresult, even when the motion limiters 2382, 2384 are merely in placewithin the grooves 2372, 2374 of the movable head 2300 without beingphysically joined to the movable head 2300, the motion limiters 2382,2384 may be physically trapped within the grooves 2372, 2374. Inparticular, the motion limiters 2382, 2384 may be trapped within thedovetail grooves 2372, 2374 in such a way as to prevent motion of themotion limiters 2382, 2384 downward in the illustrated orientation. Themotion limiters 2382, 2384 may furthermore be secured within the grooves2372, 2374 by a weld (not illustrated), or alternatively by otherjoining means such as adhesive. A weld could be created, such as bylaser welding, electron beam welding or any other suitable form ofwelding, at any suitable location where an edge or surface of motionlimiter 2382, 2384 is close to an edge or surface of movable head 2300,and where such edges or surfaces are physically accessible fordeposition of energy during welding.

Such welding may be performed either with or without adding ofadditional material during welding. Thus, there may be a primaryretention mechanism or load path that comprises the interaction betweenthe grooves 2372, 2374, and the motion limiters 2382, 2384 in the mannerof physical trapping so as to resist or prevent downward motion of themotion limiters 2382, 2384 with respect to the movable head 2300, andthere may be a secondary retention mechanism that comprises the weld orthe joining of the motion limiters 2382, 2384 to the movable head 2300.The weld or adhesive or joining or similar securing mechanism may anchorthe motion limiters 2382, 2384 in place with respect to the longitudinaldirection of the groove 2372, 2374 and the longitudinal direction of themotion limiters 2382, 2384. The weld or adhesive or joining or similarsecuring mechanism may further serve some role, although not necessarilya major role, in the actual transfer of load between the motion limiter2382, 2384 and the movable head 2300.

FIG. 27A shows a movable head 2300 containing two motion limiters 2382,2384, in a three-dimensional view from slightly below the movable head2300. FIG. 27B is an illustration similar to FIG. 27A, except that themotion limiters 2382, 2384 are removed. In FIG. 27C there areillustrated two motion limiters 2382, 2384 as they would be positionedin the assembled movable head 2300, but for clarity of illustration thebody of the movable head 2300 is omitted so that only the two motionlimiters 2382, 2384 are shown. In this illustration, the dovetail anglesof each motion limiter 2382, 2384 are labeled, and they correspond tocomplementary features of the dovetail features of the grooves 2372,2374. Finally, FIG. 27D shows a single motion limiter 2372 in adifferent orientation suitable to show certain features of the motionlimiter 2372. In particular, it can be noted that motion limiter 2372may have, and is illustrated as having, a flat edge 2388. This edge 2388or a corner associated with it may interact with shaft 2110 of screw2100.

For further illustration, FIG. 27E and FIG. 27F show the movable head2300 together with one motion limiter 2384 that is in place and theother motion limiter 2382 that is displaced along the direction ofmotion according to which motion limiter 2382 would be advanced intoslot 2372. In FIG. 27E, which is a perspective view, the viewingdirection is along the direction of advancement, and motion limiter 2382is displaced far enough back to provide an apparent difference in sizedue to perspective. In FIG. 27F, which is a view more from below, motionlimiter 2382 is displaced only to the point where it begins to makecontact with movable head 2300.

One or both of the motion limiters 2382, 2384 may have an edge 2388 thatfaces the shaft 2110 of the screw 2100, and that edge 2388 may determinethe geometry of motion limitation imposed on the screw 2100. Asillustrated in FIG. 28, if there are two motion limiters 2382, 2384 andboth of them have screw-shaft-facing edges that are substantiallystraight and are located close to the screw shaft 2110, then theallowable range of motion of the shaft 2110 of the screw 2100 may besubstantially within a plane as illustrated, i.e., what is referred toas uniplanar. It can further be appreciated that, if there are twomotion limiters 2382, 2384 and both of them have screw-shaft-facingedges that are substantially straight and have a certain clearance withrespect to the screw shaft 2110, then the allowable range of motion ofthe shaft 2110 of the screw 2100 will be approximately uniplanar with alittle bit of play perpendicular to the plane of the uniplanar motion.

In various illustrations herein, there are illustrated two differentkinds of movable head. One difference is a difference in the externalshape. The movable head design shown in FIG. 29A has an externalcross-section that is roughly cylindrical in cross-section (takenperpendicular to the longitudinal axis of the movable head), and themovable head design shown in FIG. 29B has an external cross-section thatis roughly rounded-square in cross-section (taken perpendicular to thelongitudinal axis of the movable head). Also, the movable head designshown in FIG. 29A has an instrument interface feature that is a simpleracetrack-shaped recess 2391, while the movable head design shown inFIG. 29B has an instrument interface that comprises a dovetail groove2390A, 2390B (not to be confused with the dovetail groove 2372, 2374that receives the motion limiters 2382, 2384). In practice, the movablehead design shown in FIG. 29A might be manufactured of a titanium alloy,while the movable head design shown in FIG. 29B might be manufactured ofa stainless steel alloy.

Most generally, there could be any combination of external cross-sectionshape of the movable head, any design for an instrument interface to themovable head, any choice of material, and any choice as far asconfiguration of limiters (described elsewhere herein).

D-Planar Screw

Referring now to FIGS. 30A-30D and FIGS. 31A, 31B, in an embodiment ofthe invention, there may be provided a movable head 3300 assembled to ascrew 3100 having shaft 3110 that defines a space of allowable positionsfor the screw shaft that has a boundary that is not a simple circularboundary. Such perimeter of the boundary that defines or limits themotion of the screw shaft 3110 with respect to the movable head 3300 maybe defined by a portion that is a straight line and a portion that is acurve. Such a curve may be a portion of a circle. Such a range ofallowable positions of the screw shaft is illustrated in FIGS. 31A and31B.

Such a range of motion may be achieved by a movable head 3300 that has amotion-limiting edge such that for a portion of the motion-limitingperimeter there is provided a motion limiter 3384, which may provide astraight-line limiting edge if desired, while for another portion of theon the opposite side of the mid-plane, the motion of the screw shaft3110 with respect to the movable head 3300 may be defined by an edgethat is or includes a portion of a circle.

In particular, the straight-line portion of the motion-defining edge onone side of the mid-plane of the movable head 3300 may be defined by amotion limiter 3384, while the portion of the motion-limiting edge thatis a portion of a circle may be defined by the body of the movable head3300 with no presence of a separate motion limiter. The motion limiter3384, which may occur on only one side of the movable head 3300 but notthe other side, may be similar to the motion limiter 2382, 2384described elsewhere herein.

It is also possible that the motion limiter 3384 (or similarly, 2382,2384), which has been illustrated here as having an edge that isstraight, could have an edge that is some other shape. The same may betrue for the sub-motion-limiters 382, 384 described elsewhere herein.

In FIG. 30, what is illustrated as the D-planar design has a movablehead that substantially corresponds to the first design, FIG. 29A,rather than the second design in FIG. 29B. However, it is to beunderstood that the D-planar features of FIG. 30 could similarly be usedwith the second design or with any other design details of the movablehead 3300.

FIG. 31A and FIG. 31B illustrate a range of possible positions of theshaft 3110 with respect to the movable head 3300, for the D-planardesign of FIG. 30.

In any embodiment of the invention, there may be provided a collet 3200as illustrated in FIG. 32A and FIG. 32B. In understanding this collet3200, it may be helpful to understand that in a movable-head screw thatcontains a collet surrounding the spherical screw head, it is possiblethat the angular orientation of collet 3200 with respect to movable head3300, with respect to the longitudinal axis of the collet 3200, may beunknown. Even if the assembly may be assembled with the collet in aknown angular orientation, it may be unclear if the collet will alwaysremain in that same orientation. With such angular orientation beinguncertain, it is possible that in a final installed and tightenedsituation, a spinal rod 400 may rest on the solid portion of the lip3250, or alternatively it is possible that a spinal rod 400 may sit onthe gap that may occur at a slot in the collet. These two differentsituations, either of which could possibly occur, could possibly resultin a difference in the physical location of the spinal rod relative tothe movable head 3300, and even possibly a difference in the path ofload transfer from the spinal rod 400 to the movable head 3300.

For the collet as illustrated in FIG. 32A-32B, the collet may have atone end a lip 3250, or, whether or not a lip is present, may have a flatsurface at one end. As illustrated in FIG. 32A, the collet may beprovided with slots 3212 entering from a first or proximal end of thecollet and slots 3214 entering from a second or distal end of thecollet. When viewed looking at the lip 3250 from above the collet, theremay be seen gaps in the lip or flat surface. The number of those gapsmay be an odd number, so that it is not possible for the spinal rod tosimultaneously contact gaps at one location on the lip 3250 of thecollet 3200 and also a diametrically opposed location on lip 3250.

Also, as best illustrated in FIG. 32B, the gaps 3212 at the end of thecollet that has the lip 3250 may be oriented in a non-radial direction.It is further possible that the width of the gap 3212, the thickness ofthe lip 3250 in a radial direction, and the angular orientation of thegap 3212, interact with each other such that any radial line(representing a line of possible contact with spinal rod 400) has tointersect at least a portion of the lip 3250.

The number of slots entering from the first end may be different fromthe number of slots entering from the second end. In particular, thenumber of slots 3214 entering from the distal end or the end that doesnot have the lip 3250 may be greater than the number of slots 3212entering from the proximal end or the end that has the lip 3250 or flatsurface. For example, for the number of slots 3214 entering from the endthat does not have the lip 3250 may be twice the number of slots 3212entering from the end that does have the lip 3250.

Of course, the collet 3200 described herein could be used with any ofthe screw embodiments described herein. Although embodiments of theinvention have been illustrated comprising a collet that providesfriction to retain positioning of the screw shaft with respect to themovable head, it would also be possible to create a similar screwassembly that does not have a collet or friction by omitting the collet.

Embodiments of the invention have been described herein having adovetail relationship between the motion limiter and the movable head,specifically the groove within the movable head. It can be understoodthat a dovetail joint is just one of various possible geometries thatallow the motion limiter to slide in to the movable head. For example,it is possible that a step joint having generally perpendicular sides,which may be referred to as a shelf or shelf joint, could be used. Moregenerally, it is simply necessary that a proximal dimension of themotion limiter or sub-motion-limiter be greater than a correspondingdistal dimension of the groove in which the motion limiter orsub-motion-limiter occupies. This provides a mechanical support orinterlock to prevent the motion limiter or sub-motion-limiter from beingurged out of the movable head. As described elsewhere herein, suchmechanical support can be supplemented by a joining such as welding.

It can be understood that in an embodiment such as the embodiment ofFIGS. 1-17 and the embodiments of FIGS. 26-32C), the screw 100 is ableto be rotated arbitrarily about its own longitudinal axis 140 withrespect to the movable head 300. This means that the angular rotation ofthe screw 100 into bone can be selected arbitrarily, and therefore theelevation of the screw head 130, with respect to bone into which thescrew 100 is the screwed, can be adjusted or chosen in a continuousmanner. For some embodiments of the present invention (such as theembodiment of FIG. 1-17 and the embodiments of FIG. 26-32C), it ispossible to adjust the elevation of the screw head 130, relative to thelocal bone, in a continuous manner, while still providing the restrictedtype of motion of the movable head relative to the screw shaft asdescribed herein. Any screw described herein may be cannulated, such asfor accommodating a K-wire or for delivery of a liquid such as cement tothe interior bone region. If cannulation of the screw is provided,fenestration of the walls of the screw is also possible.

The foregoing description of structures and methods has been presentedfor purposes of illustration. It is not intended to be exhaustive or tolimit the invention to the precise steps and/or forms disclosed, andobviously many modifications and variations are possible in light of theabove teaching. Features described herein may be combined in anycombination. Steps of a method described herein may be performed in anysequence that is physically possible. It is understood that whilecertain forms of a uniplanar the screw have been illustrated anddescribed, it is not limited thereto and instead will only be limited bythe claims, appended hereto. All referenced documents are incorporatedby reference herein.

While several inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto; inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

The invention claimed is:
 1. A spinal screw apparatus, comprising: ascrew shaft and a screw head fixedly attached with said screw shaft,wherein said screw head comprises a portion of a sphere, wherein saidscrew shaft has a longitudinal axis; and a movable head comprising a topportion and a bottom portion and a concave interior larger than saidscrew head, and being movable with respect to said screw head, saidmovable head having a through-passageway, said movable head having aU-trough through said top portion, wherein said U-trough includes aU-trough axis; wherein said through-passageway is bounded by an interiorwall, wherein a first portion of said interior wall intersects with afirst planar bottom surface of said movable head at a first edge portionthat is a portion of a circular arc, and a second portion of saidinterior wall intersects with a second planar bottom surface of saidmovable head at a single second edge portion that is a straight line. 2.The apparatus of claim 1, further comprising a collet interposed betweensaid screw head and said concave interior of said movable head; whereinsaid collet bears frictionally against said screw head and said movablehead sufficiently to retain an angulation setting against change ofangulation due to a force exerted by the weight of respectivecomponents.
 3. The apparatus of claim 1, wherein said bottom portioncomprises a recess suitable to receive a portion of a collet.
 4. Theapparatus of claim 1, wherein said U-trough axis is parallel to saidstraight line.
 5. The apparatus of claim 1, wherein said second planarbottom surface of said movable head and said first planar bottom surfaceof said movable head are in different planes.
 6. The apparatus of claim1, wherein said second planar bottom surface of said movable head andsaid first planar bottom surface of said movable head are parallel toeach other.
 7. A spinal screw apparatus, comprising: a screw, comprisinga shaft and a screw head fixedly attached with said shaft, wherein saidscrew head further comprises a portion of a sphere; and a movable headcomprising a top portion and a bottom portion and a concave interiorlarger than said screw head, and being movable with respect to saidscrew head, said movable head having a U-trough through said topportion, wherein said U-trough includes a U-trough axis; wherein saidmovable head comprises a through-passageway bounded by an inner wall,wherein near a bottom of said through-passageway, said inner wallcomprises a first portion that is a circular cylindrical surface havingan axis that is in an axial direction through said movable head andcomprises a single second portion that is a planar surface that isparallel to said axial direction.
 8. The apparatus of claim 7, furthercomprising a collet located within said movable head and at least partlysurrounding said screw head.
 9. The apparatus of claim 7, wherein saidcylindrical surface is located opposite said planar surface.
 10. Theapparatus of claim 7, wherein an axis of said cylindrical surface isparallel to said planar surface.
 11. The apparatus of claim 7, whereinsaid U-trough axis is parallel to said planar surface.
 12. A spinalscrew apparatus, comprising: a screw, comprising a shaft and a screwhead fixedly attached with said shaft, wherein said screw head furthercomprises a portion of a sphere; and a movable head comprising a topportion and a bottom portion and a concave interior larger than saidscrew head, and being movable with respect to said screw head, whereinsaid movable head has a U-trough through said top portion, wherein saidU-trough includes a U-trough axis; and wherein said movable head has abottom opening through said bottom portion, wherein said bottom openinghas a contact perimeter shape that is defined by points of contact ofsaid shaft and said screw head for all positions that result in contactbetween said shaft and said screw head, wherein said contact perimetershape comprises a curved portion and a single straight portion thatconnects with said curved portion.
 13. The apparatus of claim 12,wherein said straight portion of said contact perimeter shape isparallel to said U-trough axis.
 14. The apparatus of claim 12, whereinsaid contact perimeter shape comprises said single straight portion, anda first curved transition portion that follows from said single straightportion, and said curved portion that follows from said first curvedtransition portion, and a second curved transition portion that followsfrom said curved portion and further connects to said single straightportion.
 15. The apparatus of claim 12, wherein a length of said singlestraight portion is less than a diameter of said curved portion.
 16. Theapparatus of claim 12, wherein said single straight portion lies in afirst plane and at least a portion of said curved portion lies in asecond plane, and said first plane and said second plane are differentfrom each other and are parallel to each other.
 17. The apparatus ofclaim 12, wherein said single straight portion is an edge of a motionlimiter, wherein said movable head comprises a dovetail groovecomplementary to said motion limiter, wherein said motion limiter andsaid dovetail groove have a longitudinal direction that is parallel tosaid U-trough axis.
 18. A spinal screw apparatus, comprising: a screw,comprising a shaft and a screw head fixedly attached with said shaft,wherein said screw head further comprises a portion of a sphere; and amovable head comprising a top portion and a bottom portion and a concaveinterior larger than said screw head, and being movable with respect tosaid screw head, wherein said movable head has a U-trough through saidtop portion, wherein said U-trough includes a U-trough axis; and whereinsaid movable head has a bottom opening through said bottom portion,wherein said bottom opening has a shape that is defined in part by anedge of said movable head and in part by a single motion limiter,wherein said single motion limiter is elongated and said movable headcomprises a dovetail groove, wherein said single motion limiter iscomplementary to said dovetail groove.
 19. The apparatus of claim 18,wherein said single motion limiter has a straight edge facing saidbottom opening.
 20. The apparatus of claim 18, wherein said singlemotion limiter has a longitudinal direction that is parallel to saidU-trough axis.